Older adults with multiple chronic diseases are at high risk for both disability and adverse clinical events, outcomes that can be improved with physical activity, but there have been no trials to establish physical activity recommendations or clinical guidelines for this vulnerable population. Older adults with high comorbidity are a rapidl expanding subgroup, and thus there is a pressing need to develop effective approaches to motivate maintenance of physical activity to improve outcomes. A recent randomized controlled trial conducted by the applicant and mentors established the efficacy of inducing positive affect-a feeling of happiness and well-being-in motivating physical activity in older adults with cardiovascular disease, but the effect was not sustained beyond six months in older adults with multiple chronic diseases. Additional data shows that participants with a Charlson Index e 3 who maintained low levels of activity for 1 year had significantly lower rates of major clinical event t 2 years. The candidate's long-term goal is to become an independent clinical investigator in geriatric behavioral medicine focused on improving the health and quality of life of older adults with multiple chronic illnesses. The overall objective of this project, which is the next step towad that goal, is to leverage the initial successes achieved by the Positive Affect Induction for Regular Exercise (PAIRE) intervention for long-term maintenance of physical activity, targeted specifically to older adults with multiple high-risk chronic diseases. The central hypothesis is tht a tailored PAIRE intervention, customized to address the unique and complex needs of older adults with a Charlson Index e 3, will lead to sustained increases physical activity when compared to an educational control, even among those who have interval medical events or high depressive symptoms. Aim 1 is to adapt the PAIRE intervention to older adults with multiple high-risk chronic diseases. The approach will rest upon a novel and rigorous sequential mixed methods strategy to identify key psychosocial and clinical factors that mediate and moderate maintenance of physical activity in older adults with multiple high-risk chronic diseases, followed by focus groups with patients and community-based providers to assess the acceptability of potential intervention components. Aim 2 is to pilot test the new PAIRE intervention that is specific to older adults with multiple high-risk chronic illnesses. This work s innovative because it will translate the benefits of a proven intervention focused on positive affect to increase physical activity in older adults with multiple high-risk chronic illnesses, one that is tailored to the clinical and psychosocial challenges of this particularly vulnerable population. This work is significant because an effective intervention promoting physical activity will improve outcomes for older adults with multiple high-risk chronic diseases, and currently one does not exist. This project is expected to have an important positive impact because it will result in a new validated PAIRE intervention, while both positioning the candidate to submit a competitive R01 application as Principal Investigator, and enabling a novel and clinically important trajectory of work in geriatric behavioral medicine.